1. Field
Embodiments of the present invention relate to sockets for coupling integrated circuits to printed circuit boards, and in particular to land grid array (LGA) sockets having separate geometries for power delivery and signal contacts.
2. Discussion of Related Art
A land grid array (LGA) socket is a common connector used to couple an integrated circuit (IC) package to a printed circuit board (PCB. FIGS. 1A through 1E show an exploded view of a typical known LGA IC package-socket-PCB assembly 100.
FIG. 1A shows a printed circuit board (PCB) 102, FIG. 1B shows the top side (1C package side) of an LGA socket body 104. LGA contacts 106 shown in FIG. 1C fit into the socket body 104. FIG. 1D shows the IC package 108 as viewed from above as though looking through the IC package 108. FIG. 1E shows details of a portion 110 of the PCB 102. The socket assembly (i.e., the socket body 104 with the contacts 106 inserted), which is shown as a bottom view, is soldered to the PCB 102, which is shown as a top view. The IC package 108 mounts to the top side of the socket body 104.
The contacts 106 fit into slots 112 on the socket 104. Each contact 106 has a contact pad 114 that is soldered to a corresponding solder pad 116 on the PCB 102. Each contact 106 also has a contact pin 118 that mates to corresponding lands 109 on the IC package 108.
The PCB 102 has a signal delivery area 120 and a power delivery area 122. The socket body 104 has a signal delivery area 124 and a power delivery area 126. The IC package 108 has a signal delivery 128 area and a power delivery area 130. Each of the signal delivery areas corresponds to the other signal delivery areas such that input/output (I/O) signals (such as data and address signals) coming from signal planes in the PCB are electrically coupled to the appropriate solder pad 116, contact 106, and socket body 104 land. Likewise, each of the power delivery areas corresponds to the other power delivery areas such that power (VCC) and ground (VSS) coming from power and ground planes in the PCB 102 are electrically coupled to the appropriate solder pad 116, contact 106, and socket body 104 land.
One characteristic of the conventional LGA IC package-socket-PCB assembly 100 is that the contact design in the power delivery areas is the same the contact design in the signal areas (i.e., the contact 106). The contacts in the power delivery areas do not have the same function as the contacts in the signal areas, however. For example, the contacts in the power delivery areas carry high currents and the contacts in the signal areas carry low currents. Increased current density through the contacts 106 positioned in the power delivery area 126 may create self-heating which may increase contact 106 resistance and limit power delivery to the IC package 108. As high performance components consume more power and current, electrical resistance of the contacts 106 may limit power delivery to such components.
An existing approach to reducing current density through the contacts 106 is to allocate more contacts 106 in the LGA IC package-socket-PCB assembly 100 for power delivery, i.e., increase the size of the power delivery area 126. Increasing the size of the power delivery area 126 reduces the size of the signal delivery area 126, however, which may mean that the number of contacts 106 available for signals is reduced.
Another existing approach is to add more contacts 106 to the assembly 100. More contacts 106 means that the socket assembly is larger, however, and that the IC package 108 is larger. Additionally, more contacts 106 generally requires greater IC package to socket insertion force in order to maintain an effective IC package to socket interface resistance. This greater insertion force can further complicate effective enabling design.
Another characteristic of the conventional LGA IC-socket-PCB assembly 100 is that the body of the socket 104 is made from injection-molded plastic and each slot 112 is injection molded. This introduces limitations on contact 106 spacing, which can also introduces limitations on PCB solder pad 116 spacing and IC package land 109 spacing. Also, if more pins are to be added, the individual parts of the LGA IC package-socket-PCB assembly 100 are more expensive.
The socket assembly portion 110 illustrates this point. The portion 110 includes channels 132. The channel 132 has a length 134 and a set of slots 112, lands 109, contacts 106, and solder pads 116. The channel 132 has a length of approximately 10.16 mm or more. Within that length the channel 132 has approximately eight to nine slots 112, lands 109, contacts 106, and solder pads 116. Also within that length the channel 132 has a pitch (e.g., slot 112-to-slot 112, land 109-to-land 109, and contact 106-to-contact 106) of approximately one millimeter (mm). Because of the slots 112 are injection molded individually, the LGA IC package-socket-PCB assembly 100 is so limited.